1. Field of the Invention
This invention relates generally to automatic recognition of facial expressions, and more particularly, to automatic facial expression recognition that is invariant to the head orientation (aka, head pose).
2. Description of the Related Art
A facial expression is a visible manifestation of the affective state, cognitive activity, intention, personality, and/or psychopathology of a person. Facial expressions convey non-verbal communication cues in face-to-face interactions. These cues may also complement speech by helping the listener to elicit the intended meaning of spoken words. As a consequence of the information they carry, facial expressions not only help in interpersonal communications but also play an important role whenever humans interact with machines.
Automatic recognition of facial expressions may act as a component of natural human-machine interfaces. Such interfaces could enable the automated provision of services that require a good appreciation of the emotional state of the person receiving the services, as would be the case in transactions that involve negotiations. Some robots can also benefit from the ability to recognize facial expressions. Automated analysis of facial expressions for behavior science or medicine is another possible application domain.
However, in current automatic facial expression recognition (AFER) systems, the output tends to vary with the orientation of the head. The orientation of the head may be determined by the position of the camera relative to the head, and may be expressed by the three Euler angles (yaw, pitch, roll). For example, commercially available AFER systems typically will assign different smile probability values for the same facial expression captured from different points of view.
Therefore, there is a need for AFER systems that can provide facial expression recognition that is invariant to changes in the head pose.